This invention relates generally to electrical device packages and more particularly to electrical device packages for microwave integrated circuits.
As is known, microwave circuits such as amplifiers are increasingly being fabricated in the form of monolithic integrated circuits (MIC's) which are mounted in a hermetically sealed package. The integrated circuit, which may be, for example, a microwave monolithic integrated circuit (MMIC) amplifier, is typically mounted on a carrier which comprises microstrip circuitry, that is, circuitry comprising strip transmission lines disposed on a first surface of a dielectric substrate with a single ground plane being disposed on the second surface of the substrate, for coupling microwave signals to and from the MIC. The MIC package typically comprises a hermetically sealed housing typically having one or more microwave coaxial feed-through connectors mounted in the walls thereof for coupling microwave signals to and from the inputs and outputs of the MIC device via the microstrip circuitry disposed on the MMIC carrier.
Such coaxial connector is generally cylindrical in shape and conventionally comprises a generally circular cross-sectioned center conductor disposed coaxially in an insulator, such as glass, and extending longitudinally through the cylindrical connector. Surrounding the glass insulator is a metal cylindrical shell which passes through the wall of the package housing and is hermetically sealed thereto, such as by soldering. The center conductor protrudes beyond the metal shell externally to the package and is adapted to receive a microwave transmission line, such as a microstrip transmission line, at, for example, a "lap joint" between the center conductor and transmission line. The center conductor typically extends a short distance into the package beyond the metal shell. Conventionally, the package housing comprises a microstrip input/output stage, which provides electrical transition and impedance matching between the coaxial transmission line mode of the coaxial connector (and microwave transmission line circuitry external to the package housing) and the microstrip transmission line mode of the MMIC carrier inside the package. The input/output circuit section comprises a microstrip transmission line section soldered to the package housing via the ground plane thereof. A first end of the input/output circuit underlies the protruding center pin of the package coaxial connector. The center pin is soldered to the strip transmission line of the input/output circuit. The second end of the input/output circuit is disposed adjacent to the microstrip monolithic integrated circuit carrier. Electrical connection is made therebetween by a short, flexible member of electrically conductive ribbon, such as gold ribbon, between the transmission lines of the input/output section and the integrated circuit carrier. The dimensions of the package connector center pin, the input/output circuit transmission line and the ribbon member are selected to provide impedance matching at the characteristic impedance, such as 50 ohms, throughout the coaxial-to-microstrip transition of the MIC package.
While such arrangement for providing a transition from a coaxial transmission line mode to a microstrip transmission line mode is adequate in some applications, the requirement for providing a separate input/output transmission line circuit section for each package coaxial connector increases the complexity of the MMIC package by requiring each package to contain more parts. Additional machining of the package housing is required to accommodate the input/output circuit sections, and the overall package size is increased due to the presence of such input/output sections. Also, the soldered or welded lap joint connection between the coaxial connector center pin and the input/output circuit transmission line is rigid and thus may crack and fail due to thermal expansion or contraction of the input/output circuit.